Typical thin film read heads are located between shields. The shields improve head performance by shielding stray magnetic flux from the sensor element. Gap layers electrically insulate the shields from the sensor element and from abutting lead structures.
As read head structures become smaller to improve aerial density, it is desirable to reduce the thickness of the insulative gap layers to optimize head sensitivity. Although reducing the thickness of the gap layers improves sensitivity by reducing the distance between the sensor and the shield, it also allows lead structures deposited lateral to the sensor element to more easily short to the shields.
Because shield-to-shield spacing is not as critical away from the sensor element, it is not necessary to have thin gaps away from the sensor element. As such, extra gap layers typically are deposited over the gap layers-away from the sensor element to increase gap thickness away from the sensor element. This reduces shorting between the lead structures and the shields.
An example of such structure is disclosed in U.S. Pat. No. 5,568,335, by Fontana, et al., issued Oct. 22, 1996, entitled MULTI-LAYER GAP STRUCTURE FOR HIGH RESOLUTION MAGNETORESISTIVE READ HEAD, herein incorporated by reference in its entirety. In such a read head, the extra gap layer is deposited over the gap layer lateral to and away from the sensor element. Although this reduces shorting between the leads and shields, the present inventors have found such structures difficult to reliably manufacture with submicron track widths. Sub-micron track width is necessary for high track density applications greater than about 15 Kilo tracks per inch and aerial densities greater than about 7 Giga bits per square inch. Such a structure, therefore, while improving reliability of the read head, proves an impediment to high aerial density.
The present invention provides a thin film read head having an extra gap layer inset in the lower shield layer. In a preferred embodiment, a pedestal is formed from a lower shield layer, such as by ion milling the lower shield layer. With this embodiment, the lower extra gap layer is formed adjacent the pedestal so that the top surfaces of the extra gap layer and the pedestal are at approximately the same level. This allows for deposition of generally planar lower gap and sensor layers over the lower extra gap layer, reducing surface topography, thus improving control of resist deposition and patterning.
With the preferred method, a sensor element is defined from the generally planar sensor layer, using a bilayer resist structure. The generally planar surface inhibits resist pooling, which could otherwise degrade resist structure formation, and allows for more uniform resist deposition. As such, smaller, more robust resist structures may be formed on the sensor layer to define a smaller track width sensor element. This allows manufacture of reduced track width devices while providing extra gap material for protection from lower shield-to-lead shorting.
In a typical embodiment, the thin film read head of the present invention may have a spin valve type sensor element with leads electrically coupled to the sensor element, an upper gap layer extending between the sensor element and the upper shield layer, and an upper extra gap layer disposed between at least a portion of the leads and the upper shield layer. Furthermore, the thin film read head typically is embodied in a data storage and retrieval apparatus having a merged read/write head assembly.